The present invention relates to a method and apparatus for making a rod from powdered metal, and more particularly to a new and novel method for continuously forming the rod from powdered metal and to a new and novel apparatus for carrying out the method.
The present method and apparatus are an improvement of the method and apparatus described in U.S. Pat. application, Ser. No. 448,819 filed Apr. 7, 1974 assigned to the assignee of the present invention and which is incorporated herein by reference thereto.
By the present invention it is proposed to provide an improved method for continuously forming a bar from a powdered metal wherein successive separate quantities of powdered metal are compacted by compacting means axially movable in a generally horizontally disposed die having a cavity of fixed cross-sectional area. The successive quantities of powdered metal are compacted into bar segments and bonded to each other to form a length of green compact bar. The green compact bar is incrementally forced out of the die such that a length thereof is frictionally retained within the die to serve as a stopper against which a succeeding quantity of powdered metal is compacted. The frictional resistance force between the cavity wall and the length of the bar defining the stopper is measured. This measurement is used to determine if the frictional resistance force corresponds to the compacting force required to compact the quantity of powdered metal into a bar segment having desired physical characteristics. If the frictional force deviates from the required force, the length of travel of the compacting means is changed so that the volume of powdered metal introduced into the die cavity is varied until it is compressed into a green bar segment having the desired green strength physical characteristics.
In accordance with the present invention, the apparatus includes a feed tube that communicates with a source of powdered metal and is axially aligned with the die cavity in which the powdered metal is compressed. A punch is axially reciprocable within both the die cavity and the feed tube and serves to compact the powdered metal. The punch travels between a retracted position within the feed tube and a compacting position within the die cavity. The compacting position of the punch within the die cavity is maintained constant while the retracted position in the feed tube is varied so that the volume of powdered metal introduced therein is varied. In this manner, the volume of powdered metal compacted in the die cavity is varied until a bar segment is formed having the desired green strength characteristics. The volume of powdered metal is thereafter maintained substantially the same so that each segment forms a bar of uniform green strength characteristics along its length.
The green compacted rod formed in the continuous manner as described above is then sintered to improve the physical characteristics after emerging from the die. Preferably the sintering is performed by induction heating means.
After sintering the rod may also be swaged or otherwise hot worked to further increase the density thereof.
Further features of the invention will hereinafter appear.